There has been developed the widespread practice of utilizing photogrammetry, as well as automated theodolites, for a measurement tool for determining specific locations upon numerous industrial devices and industrial equipment; such as, among others tooling utilized in the construction of industrial products and articles with special reference to aircraft and automobiles, as well as components thereof. Light reflective targets are positioned at predetermined locations upon the specialized tooling in accordance with a pre-arranged pattern so that the precise relationship of the preselected locations therefor may be measured and/or verified. The periodic photogrammetric reproduction of the target pattern permits of facile reference to the original preselected target inter-relationship to assure of appropriate quality thereby allowing of elimination of any deformation or deflection that may have occurred through usage. The utilization of photogrammetry is appropriate for frequent inspection obviating the time-consuming, costly inspection by gauging which necessarily requires a master gauge for direct physical application involving the utilization of skillfully trained individuals. Thus, any divergence from the essential target relationship may be promptly effected with tool down-time minimized or eliminated and cost effectiveness greatly enhanced.
The targets utilized heretofore have consistently mounted, as often within a shallow recess, a light reflective tape* which constitutes a substrate upon the exposed face on which is adhered by a suitable glutinous material an assembly of light reflective granules, such as glass beads, which may have a diameter as in the order of 0.003 inches; being generally referred to as target dots. The opposite face of the tape is coated with a suitable adhesive, as in a layer in the range of 0.001 inches in thickness within the shallow recess formed in the target body. Such target thus constitutes what might be referred to as engineering points on the tooling, but, in addition thereto, have a wide range of uses for measuring, verifying, checking, and surveying intervening distances or inter-relationships between the target distances which may be in feet, inches, thousandths of an inch. FNT *Retro-reflective tape of this type is produced by 3M Company.
However, with targets of the type heretofore utilized there have been recognized certain serious problems. One of such has been caused by a certain instability due to the adhesive on the rear side of the substrate and also due to the relatively small size of the "dot", as a result of the inherent nature of the customary adhesive utilized upon the tape substrate. The critical location of the generally dot-forming granules is manifestly readily disturbed through inadvertent movement of the tape which may be caused by accidental forces impacting thereon.
Another problem results from the constitution of the retro-reflective material, that is, the granules, which are similar in general physical configuration to the discrete particles of sand as found upon sand paper, being coarse and uneven, so that a sharp, distinct, crisp edge on the granule or bead-like target portion is consistently attained. Such beads, which are adhesively secured to the tape substrate and being customarily of glass, may be severed rather easily, crushed, inadvertently removed, etc., when the retro-reflective tape is cut during the manufacturing process, all resulting in a jagged, irregular edge so that sharp deformation of the light-reflective "dot" or zone is denied. It will be appreciated that when one is concerned with the precise measurements sought by photogrammetry these aforesaid problems are indeed serious since the least displacement or inaccuracy in positioning, as well as irregularities in the edges of the light reflective beads zone cause a very grave effect when utilizing the photogrammetric reproduction for verifying or measuring purposes. Furthermore, such problems severely diminish the accuracy of the determinations of the bead light reflective "dot" or zone with consequent commensurate inaccuracies in the measurement.